1. Field of the Invention
This invention relates generally to a magnetic recording disk with pre-patterned surface features of elevated lands and recessed grooves or trenches, and more particularly to such a disk with a planarized surface.
2. Description of the Related Art
Conventional magnetic recording hard disk drives use either horizontal recording wherein the magnetized regions that define the magnetically recorded data bits are oriented in the plane of the recording layer on the hard disks, or perpendicular recording wherein the magnetized regions are oriented perpendicular to the plane of the recording layer. The conventional disk is a “continuous-media” (CM) disk wherein the recording layer is a continuous layer of magnetic material that becomes formed into concentric data tracks containing the magnetically recorded data bits when the write head writes on the magnetic material. The recording layer also includes a pre-recorded pattern of servo sectors that are used to position the read/write heads to the desired data tracks and maintain the heads on the data tracks during reading and writing. The conventional CM disk has a protective overcoat, typically formed of amorphous carbon, like diamond-like carbon (DLC), that covers the recording layer and provides a generally smooth planar surface. The read/write heads are located on air-bearing sliders that are supported above the smooth disk surface on a thin film of air or “air-bearing” as the disk rotates.
A variation of a CM disk is a “discrete-track media” (DTM) disk, meaning that the concentric data tracks of continuous magnetic material are radially separated from one another by concentric nonmagnetic guard bands. DTM disks are known in the art, as described for example in U.S. Pat. No. 4,912,585. In a DTM disk, the data tracks are typically elevated lands that contain magnetic material and the nonmagnetic guard bands are trenches or grooves that are recessed below the elevated lands. The nonmagnetic guard bands are either formed of nonmagnetic material or contain magnetic material but are recessed far enough below the elevated data tracks to not adversely the readback signals from the data tracks.
In addition to CM disks and DTM disks, magnetic recording disks with “bit-patterned media” (BPM) have been proposed to increase the data density. In BPM disks, the magnetizable material on the disk is patterned into small isolated data islands such that there is a single magnetic domain in each island or “bit”. The single magnetic domains can be a single grain or consist of a few strongly coupled grains that switch magnetic states in concert as a single magnetic volume. This is in contrast to conventional CM disks wherein a single “bit” may have multiple magnetic domains separated by domain walls. To produce the required magnetic isolation of the patterned islands, the magnetic moment of the spaces between the islands must be destroyed or substantially reduced so as to render these spaces essentially nonmagnetic. In one type of BPM disk, the data islands are elevated, spaced-apart pillars that are separated by nonmagnetic trenches or recesses.
DTM disks and BPM disks also require servo sectors that are angularly spaced around the disk and extend generally radially across the concentric data tracks. The servo sectors are pre-recorded patterns that cannot be written over by the write heads and that are used to position the read/write heads to the desired data tracks and maintain the heads on the data tracks during reading and writing. In both DTM disks and BPM disks, the servo sectors may be pre-patterned surface features of elevated servo blocks of magnetic material separated by nonmagnetic trenches or recesses.
There are several methods for fabricating disks with surface features of elevated lands and recessed grooves. In one technique, applicable for both DTM and BPM disks, all the required layers, including the layer or layers of magnetic recording material, are deposited on the disk substrate, typically by sputter deposition. The disk is then lithographically patterned into the desired pattern of data tracks and guard bands, as well as servo sectors. A vacuum etch process, such as ion milling or reactive ion etching (RIE), then removes the exposed magnetic recording material. This results in lands of magnetic material and nonmagnetic grooves recessed from the upper surface of the lands.
In another technique, particularly applicable for BPM disks, the disks are produced by replication from a mold via nanoimprinting. The nanoimprinting process forms not only the isolated data islands in the data tracks, but also the servo blocks in the servo sectors. In nanoimprinting, a mold or template replicates a topographic pattern of surface features onto a polymeric resist coating on the disk substrate. The disk substrate may have a dielectric coating, such as a silicon nitride film. The nanoimprinted resist pattern is then used as a mask for etching the pattern into the silicon nitride film with a fluorine plasma. After etching the silicon nitride, the resist is removed. Magnetic material is then sputter deposited over the lands and grooves. The grooves may be recessed far enough from the read/write heads to not adversely affect reading or writing, or they may be “poisoned” with a dopant material to render them nonmagnetic.
For DTM disks and BPM disks there is a need to planarize the surface topography so that the slider is maintained at a relatively constant “fly height” by the air-bearing generated by the rotating disk. Planarization is especially important to reduce or eliminate slider excitations induced by transitioning from a data to servo region or from a servo to data region. The planarization is typically accomplished by deposition of nonmagnetic fill material in the recessed grooves or trenches, followed by chemical-mechanical-polishing (CMP). However, the nonmagnetic fill material may become delaminated during CMP.
What is needed is a disk with pre-patterned surface features of elevated lands and recessed grooves or trenches that has a planarized surface where there is secure adhesion of the fill material in the grooves or trenches.